A term “supercooling” describes a phenomenon that melt or solid does not change even after it is cooled down to a temperature lower than the phase transition temperature at equilibrium state. In general, every material has its own stable state at a given temperature, so if temperature changes gradually, atoms of the substance keep abreast with the changes of temperature while maintaining its stable state at each temperature. However, if temperature changes abruptly, there is not enough time for the atoms to get into a stable state corresponding to each temperature. What happens then is the atoms either keep the stable state at a start temperature, or partially change to a state at a predetermined end temperature then stop.
For example, when water is cooled slowly, it does not freeze for some time even though the temperature is below 0° C. However, when an object becomes a supercooled state, it is a sort of metastable state where the unstable equilibrium state breaks easily even by a very small stimulus or minor external disturbance, so the object easily transits to a more stable state. That is to say, if a small piece of the material is put into a supercooled liquid, or if the liquid is subject to impact on a sudden, it starts being solidified immediately and temperature of the liquid is raised to a freezing point, maintaining a stable equilibrium state at the temperature.
Generally, foods such as vegetables, fruits, meats and beverages are refrigerated or frozen to be kept fresh. Such foods contain liquid elements such as water. If the liquid elements of the food are cooled below a phase transition temperature, the liquid elements are transited into solid elements at a predetermined time point. When the liquid elements are transited into the solid elements and the entire food is subsequently frozen, quality of the food is seriously lowered.